Electrostatic latent image transferring apparatus for use in electrophotography

ABSTRACT

An electrophotographic apparatus for transferring electrostatic latent images comprising a photosensitive drum consisting of a layer of photosensitive material on a conductive body; an insulating roller normally disposed in contact with said photosensitive drum for the purpose of transferring an electrostatic latent image formed on said layer of photosensitive material to an interposable electrostatic transfer paper consisting of a conductive paper support with an image receiving dielectric layer thereon; at least one set of paper feed rollers disposed in front of and one set disposed to the rear of said insulating roller (the rollers disposed on the side of said dielectric layer consisting of an insulating material while the rollers disposed on the side of said paper support consist of a conductive material) for feeding the electrostatic transfer paper in between said insulating roller and photosensitive drum; and a low-voltage DC power source having one terminal with the same polarity as that of the electric charge to be impressed on the photosensitive layer by corona discharge, and electrically connected with said conductive body of the photosensitive drum, while the other terminal has the opposite polarity and is electrically connected with said conductive feed rollers, said conductive feed rollers being grounded through the chassis of the apparatus and said photosensitive drum being insulated relative to the chassis of the apparatus.

United States Patent [191 Kurokawa et al.

[ ELECTROSTATIC LATENT IMAGE TRANSFERRING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY [75] Inventors: Junii'Kur'okawa; Toshio Watanabe; Tomiaki Asami, all of Tokyo, Japan [73] Assignee: Kabushiki Kaisha Ricoli, Tokyo,

Japan 22 Filed: Nov. 19, 1973 21 Appl. No.: 416,732

[30] Foreign Application Priority Data Primary Examiner-Robert P. Greiner Assistant Examiner-Kenneth C. Hutchison Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran [451 Sept. 10, 1974 [57] ABSTRACT An electrophotographic apparatus for transferring electrostatic latent images comprising a photosensitive drum consisting of a layer of photosensitive material on a conductive body; an insulating roller normally disposed in contact with said photosensitive drum for the purpose of transferring an electrostatic latent image formed on said layer of photosensitive material to an interposable electrostatic transferpaper consisting of a conductive paper support with an image receiving dielectric layer thereon; at least one set of paper feed rollers disposed in front of and one set disposed to the rear of said insulating roller (the rollers disposed on the side of said dielectric layer consisting of an insulating material while the rollers disposed on the side of said paper support consist of a conductive material) for feeding the electrostatic transfer paper in between said insulating roller and photosensitive drum; and a low-voltage DC power source having one terminal with the same polarity as that of the electric charge to be impressed on the photosensitive layer by corona discharge, and electrically connected with said conductive body of the photosensitive drum,while the other terminal has the opposite polarity and is electrically connected with said conductive feed rollers, said conductive feed rollers being grounded through the chassis of the apparatus and said photosensitive drum being insulated relative to the chassis of the apparatus.

6 Claims, 5 Drawing Figures FIG. 4

I000 ELECTROSTATIC LATENT IMAGE AREA I 950V I NON-ELECTROSTATIC LATENT IMAGE AREA 300 (400V I POTENTIAL ON PHOTO- SENSITIVE LAYER (VI TIME CORONA LIGHT TRANSFERRENCE CHARGE DECAY FIG. 5

NON-ELECTROSTATIC LATENT IMAGE AREA I4OOVI POTENTIAL ON PHOTO- SENSITIVE LAYER TIME CORONA LIGHT TRANSFERRENCE CHARGE DECAY BACKGROUND OF THE INVENTION discharge deposition; exposing .it to light to form thereon an electrostatic latent image; transferring said latent image onto an electrostatic recording vpapervand developing the thus transferred :image'xto obtain the intended image) it *is desirable that the photosensitive body be permanent-lydurable. In copying presses of this type, inasmuch as the surface of the photosensitive body never comes in contact with the developer, or

cleaner or the like, there is little chance of the durabilmechanical external force. However, if a high voltage is repeatedly applied to the layer of photosensitive material at the time of corona discharge in .an attempt to enhance the transfer of the electrostatic latent image when utilizing only .the electric field :producediby the photosensitive layer, the bodywill have its life remarkably shrten'ed,.give1rise to dielectric breakdown and become rapidly :unfit for use. Tocope with this .problem, it has been usual in the priorart Ito .utilize the .effect of the electric field produced by the electrostatic latent image at the time oftransferringithereof together with the effect of another electric fieldappliedwto the photosensitive layer from the outside of the foregoing electric fieldso asto make it'possible to perform transity of the photosensitive body being affected by .any 125 ference even when the electrostatic latent-image has a low potential to-avoid as-far as possible the used a-high potential charge on the photosensitive material.

FlG. lin the drawings is illustrative of the general electrostatic latent image transferring apparatus utilizing the foregoing synergetic effect. photosensitive drum 1 consists of a photosensitivelayer l1 and a conductive body 12. Conductive roller2'is fortransferring the electrostatic latent image formed on the photosensitive layer 11 to the electrostatic transfer paper '8 which consists of a dielectric layer and a conductive paper support. A low-voltage DC power source of 100- 500V is connected to the roller'2. Two sets of rollers 4 supply the electrostatic transferpaper 8.between the roller ,2 and the photosensitive drum l'for transferring the electrostatic latent image thereto and further sending it to a developing section 7. A corona vdischarger 5 having a high-voltage DC power source 6 of. 6-8KV and an optical system 9 are appropriatelydisposed about .drum 'l.ln -FlG.i2theatransferring section of the apparatus shown in FIG. 1 is shown on-an enlarged scale. The dielectric layer 82 of the electrostatic transfer paper 8 is incontact with the photosensitive layer 11 of the photosensitive drum 1, while the conductive paper support=8l is in contact with'the transferring roller 2. ln thisconnection, the surfaces of the photosensitivedrum l and-the transferring roller 2 are ordinarily in contact with each other, but, when an electrostatic transfer paper 8 is inserted between them, the photosensitive surface of drum land the dielectric surface of electrostatic transfer paper 8 come in contact with each other and the electrostatic charge forming the electrostatic latent image is transferred from the drum 1 to the paper 8 by virtue of the electric field working therebetween. However, actual use of this apparatus in electrostatic transferring is accompanied with various problems such as follows:

1. When there is no electrostatic transfer paper interposed, the transferring roller 2 and the surface of .pho-

tosensitive layer 11 come in direct contact with each other and an electric field of several hundred volts works on the photosensitive layer, causing partial dielectric breakdown of the photosensitive layer. Although this trouble can be avoided by impressing the voltage on the transferring roller 2 only when an electrostatic transfer paper has been inserted, yet inasmuch as the applicable electrostatic transfer papers may be of various sizes, when a relatively narrow transfer paper isinserted, the widthwise margin of the transferring roller2 comes in direct contact with the surface of photosensitive layer 11 and this direct contact area of the photosensitive layer becomes electrically vulnerable, resulting in a shortened life for the photosensitive layer.

.2. In the case where an electrostatic transfer paper 8 is sent in the direction of the arrow in FIG. 1 by means of the feed rollers 4, transference is effected and the fore end of said'transfer paper reaches the developing section 7 while the rear end thereof is still in contact with the transferring roller .2. Since the paper support 'slis-conductive, electric current runs through the base imparting a uniform electric potential thereto, and, in the fore end portion of the transfer paper, there take place a bias development on this occasion and the image comes to disappear. Even when the feed rollers 4 are grounded through the chassis of the apparatus (not shown herein), there will appear an inverse potential of several tens of volts on the paper support 81. On the other hand, as the potential of the electrostatic transfer paper subsequent to transference is volts at the most in the image area thereof, an image obtained through development will show low concentration just in the fore end portion thereof.

The foregoing troubles incident to the conventional apparatus are attributable to the fact that transferring roller2 is conductive and a voltage is applied to this conductive transferring roller and through it to the conductive support for the electrostatic transfer paper.

The object of the present invention is to make up for the foregoing defects of the prior art and to provide an improved apparatus for transferring electrostatic latent images which comprises a photosensitive layer free of dielectric breakdown and accordingly of permanent durability.

SUMMARY OF THE INVENTION The present invention involves an apparatus for transferring electrostatic latent images suited for use in .electrophotography, which comprises a photosensitive .drum consisting of a photosensitive layer on a conductive -body;.an insulating, rather than'conductive, roller normallydisposed in contact with said photosensitive layer for the purpose of transferring an electrostatic latent image formed on said photosensitive layer to an interposable electrostatic transfer paper consisting of a conductive paper support and a dielectric layer; at least one set of paper feed rollers disposed in front of and one set disposed in the rear of said insulating roller (the rollers disposed on the side of said dielectric layer consisting of an insulating material while the rollers disposed on the side of said paper support consist of a conductive material) for feeding the electrostatic transfer paper in between said insulating roller and photosensitive drum; and a low-voltage DC power source having one terminal with the same polarity as that of the electric chargeof the corona discharge to be imparted to the photosensitive layer, and electrically connected with said conductive body of the photosensitive drum, while the other terminal has the opposite polarity and is electrically connected with said conductive feed rollers, said conductive feed rollers being grounded through the chassis of the apparatus and said photosensitive drum being insulated relative to the chassis of the apparatus. In this connection, the chassis of the apparatus according to the present invention means a device for supporting the parts necessary for the apparatus, namely, the photosensitive drum, transferring roller, feed rollers, low-voltage DC power source and so on, which may further include the frame, electrifier, optical system, developing device, fixing device, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic representation of an apparatus for transferring an electrostatic latent image in accordance with the prior art.

FIG. 2 is a diagrammatic representation of the transferring section on an enlarged scale of the apparatus shown in FIG 1.

FIG. 3 is a diagrammatic representation of an apparatus for transferring electrostatic latent images according to the present invention.

FIG. 4 is a curve showing the change of surface potential on the selenium layer in Example 1, and

FIG. 5 is a curve showing the change of surface potential on the organic photoconductive layer in Example 2.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings for further elucidation of the present invention, FIG. 3 is a diagrammatic representation of an apparatus embodying the present invention. The photosensitive drum 1 is insulated relative to the chassis of the apparatus (not shown in the drawing) and this drum is charged with a voltage in the range of l00-500V having the same polarity as that of the electric charge of the corona discharge by means of a lowvoltage DC power source 3a at the time of transferring. The entire transferring roller 2a or at least the surface thereof coming in contact with the photosensitive layer 11 of the photosensitive drum 1 consists of an insulating material such as rubber, resin or the like. Accordingly, when no electrostatic transfer paper has been interposed, no voltage is set up on the photosensitive layer, and even when an electrostatic transfer paper has been interposed, only the portion of the photosensitive layer coming in contact with said transfer paper is charged with voltage, so that the troubles of the prior art are avoided. In this context, when roller 2a consists of rubber, the closeness of surface contact between the electrostatic transfer paper and photosensitive layer can be furthered. In at least one set of the feed rollers, 4a, 4b or 40, 4d, the surface of the roller disposed on the support side of the electrostatic transfer paper 8 consists of a conductive material, such as metal or conductive rubber, and is grounded through the chassis of the apparatus. The rollers 4a and 4d on the support side of transfer paper 8 when conductive function as one electrode at the time of image transference to the electrostatic transfer paper and act to impress an external voltage by means of the low-voltage DC power source 30. The rollers 4b and 4d on the side of the dielectric layer are all insulated relative to the chassis of the apparatus, so that they never exert any harmful influence electrically upon the electrostatic transfer paper and the rollers 4a and 4c on the support side. The corona discharger 5 is so devised that, even when the photosensitive layer is in a state of low potential, the discharger is provided with a high-voltage power source 6 having a potential far greater than that of said photosensitive layer, and therefore no influence is exerted upon the corona discharge, thereby permitting proper electrification of the photosensitive layer without hindrance. Further, inasmuch as one of the terminals of the low-voltage DC power source 3a has the same polarity as the polarity of the electrical charge of the corona discharge, such a power source can be taken out of a part of the high-voltage DC power source used for the corona discharge. In this case, inasmuch as the support side of the electrostatic transfer paper is always grounded by means of the conductive feed rollers 4a and 4c, no influence will be exerted thereby at the time of development and a satisfactory image will be obtained.

Some examples of particular embodiments of the present invention are as follows:

EXAMPLE I In the apparatus shown in FIG. 3, the photosensitive drum 1 employed may consist of a metal drum having a diameter of 70 mm provided with a 25 1:. thick photosensitive layer of selenium. When this selenium layer of the drum is imparted with +300V potential by a lowvoltage DC power source 30 and a corona discharge of +7.0 KV is effected by rotating the drum at a velocity of 40 rpm, the apparent surface potential of thephotosensitive drum becomes 1000V as-shown in FIG. 4. When this photosensitive layer is exposed to light subsequent thereto, the potential becomes 950V for the electrostatic latent image area and 400V for the nonelectrostatic latentimage area, while onto the electrostatic transfer paper an electrostatic charge is transferred having a surface potential of V and 0V respectively, and the developed area produces a satisfactory image.

Moreover, the selenium layer is electrified by corona discharge to the extent of a potential of only 700V in effect, and even when it comes in direct contact with an insulating transferring roller 2a, the electric field acting on the selenium layer is trifling, so that the durability of the selenium drum is remarkably improved.

EXAMPLE 2 ent surface potential on the organic photoconductive drum on this occasion will be 800V as shown in FIG. 5; As the residual potential of this organic photoconductor at the time of light decay is greater than that of selenium, application of a high external electric field at the time of image transference is attended with the transfer of the electric charge of the non-electrostatic latent image area and tends to give rise to a stained ground on the electrostatic transfer paper, but in the case of the present apparatus, application of a low potential of --200V can bring on a satisfactory result. To be precise, the transferred potential on the electrostatic transfer paper will be 90V and (W for the electrostatic latent image area and the non-electrostatic latent image area, respectively.

Further, general organic photoconductive layers become unfit for use because of the increase of spots of dielectric breakdown after repeated use of several thousand times under the condition of more than 900V in surface potential (negative potential). In the case of the present apparatus, however, inasmuch as the organic photoconductive layer is to be used by applying 600V, the durability of the organic photoconductive drum has ben improved accordingly.

What is claimed is:

1. An electrostatic latent image transferring apparatus for use in electrophotography, comprising: a photosensitive drum consisting of a photosensitive layer and a conductive body; an insulating roller disposed in contact with said photosensitive layer for transferring an electrostatic latent image formed by corona discharge and illumination on said photosensitive layer to an interposable electrostatic transfer paper consisting of a conductive paper support with an image receiving dielectric layer thereon; at least one set of paper feed rollers disposed in front of and one set disposed to the rear of said insulating roller, the feed rollers disposed on the side of said dielectric layer having an insulating surface and at least one of the feed rollers disposed on the side of said paper support having a conductive surface, for feeding the electrostatic transfer paper in between said insulating rollers and said photosensitive drum; and a low-voltage DC power source having one terminal with the same polarity as that of the electric charge of the corona discharge applied to the photosensitive layer and electrically connected with said conductive body of the photosensitive drum and the other terminal having an opposite polarity and electrically connected with the surface of said conductive feed roller, said conductive feed rollers being grounded through the chassis of the apparatus and said photosensitive drum being insulated relative to the chassis of apparatus.

2. A transferring apparatus according to claim 1, wherein said photosensitive layer of the photosensitive drum consists of selenium.

3. A transferring apparatus according to claim 1, wherein said photosensitive layer of the photosensitive drum consists of poly-N-vinylcarbozole.

4. A transferring apparatus according to claim 1, wherein the voltage of said low-voltage DC power source is in the range of IOU-500V.

5. A transferring apparatus according to claim 1, wherein both of said feed rollers on the side of said paper support are conductive.

6. A transferring apparatus according to claim 1, wherein the surfaces of said insulating feed rollers comprise rubber. 

1. An electrostatic latent image transferring apparatus for use in electrophotography, comprising: a photosensitive drum consisting of a photosensitive layer and a conductive body; an insulating roller disposed in contact with said photosensitive layer for transferring an electrostatic latent image formed by corona discharge and illumination on said photosensitive layer to an interposable electrostatic transfer paper consisting of a conductive paper support with an image receiving dielectric layer thereon; at least one set of paper feed rollers disposed in front of and one set disposed to the rear of said insulating roller, the feed rollers disposed on the side of said dielectric layer having an insulating surface and at least one of the feed rollers disposed on the side of said paper support having a conductive surface, for feeding the electrostatic transfer paper in between said insulating rollers and said photosensitive drum; and a lowvoltage DC power source having one terminal with the same polarity as that of the electric charge of the corona discharge applied to the photosensitive layer and electrically connected with said conductive body of the photosensitive drum and the other terminal having an opposite polarity and electrically connected with the surface of said conductive feed roller, said conductive feed rollers being grounded through the chassis of the apparatus and said photosensitive drum being insulated relative to the chassis of apparatus.
 2. A transferring apparatus according to claim 1, wherein said photosensitive layer of the photosensitive drum consists of selenium.
 3. A transferring apparatus according to claim 1, wherein said photosensitive layer of the photosensitive drum consists of poly-N-vinylcarbozole.
 4. A transferring apparatus according to claim 1, wherein the voltage of said low-voltage DC power source is in the range of 100-500V.
 5. A transferring apparatus according to claim 1, wherein both of said feed rollers on the side of said paper support are conductive.
 6. A transferring apparatus according to claim 1, wherein the surfaces of said insulating feed rollers comprise rubber. 